According to confidence heuristic, expressed greater confidence (certainty) leads to increased impressions of expertise and believability. So whenever you express certainty (confidence) about your position, you raise your credibility. Quite a few studies showed the value of this technique:
- One study showed that witness’s confidence predicts his or her perceived credibility (Whitley & Greenberg 1986).
- Another study showed that people are more likely to accept an advice when their advisors show a lot of confidence (Sniezek & Van Swol 2001).
- Another study compared highly confident financial advisors with moderately confident ones. Advisors who expressed certainty about their stock forecasts were perceived as more knowledgeable and were more frequently chosen (Price & Stone 2004).
Will you always boost your persuasiveness by expressing certainty? No, but the exceptions are few.
Certainty and Accuracy: Confidence Calibration
A major exception to the power of certainty is when it conflicts with accuracy. Plenty of studies show that even small dents in accuracy can damage person’s overall credibility (for example, an eyewitness’s overall credibility can be damaged by showing that he was wrong about such peripheral details as the weather at the time of an accident).
A study by Elizabeth Tenney and her colleagues shows that certainty backfires whenever a confident person is shown to be inaccurate (Tenney et al 2007). In other words, people downgrade confident speakers more than non-confident ones for any inaccuracy. So whenever there is risk that you might be inaccurate, you’re best off expressing uncertainty. And when there is little risk that you’ll be shown inaccurate, express certainty.
Uncertainty and Increased Interest in Message
Expressed uncertainty can help when it increases interest in the message. For example, studies in consumer research shows that in certain cases the effectiveness of the confidence heuristic depends on who expresses certainty. For one, expressing uncertainty may be useful when your audience considers you an expert; when an expert shows uncertainty, it usually creates unexpectedness, and unexpectedness leads to more careful processing of the message; more careful processing of the message, when the arguments are strong, will lead to more persuasion. (Of course, when the arguments are weak, more careful processing will lead to less persuasion.)
In one study (Karmarkar & Tormala, 2010), two Stanford University researchers asked subjects to read a restaurant review.
- Some subjects read the review which expressed high certainty: “I can confidently give [the restaurant] Bianco a rating of 4 (out of 5) stars.”
- Others read the review that expressed low certainty: “I don’t have complete confidence in my opinion, but I suppose I would give Bianco a rating of 4 (out of 5) stars.”
Of course, anyone would expect that the two reviews would sway differently. But what mattered here was who the reviewer was: expert or non-expert.
- Expert was described thus: Stephen Stone, a nationally renowned food critic and regular contributor to the food and dining section of a major newspaper area.
- Non-expert was described as follows: Stephen Stone, a networks administrator at a nearby community college who kept a personal Web journal.
The results were as researchers predicted:
“a nonexpert source gained interest and influence by expressing certainty, whereas an expert source gained interest and influence by expressing uncertainty.”
Unexpectedness is one of the main reasons here. We expect lay people to be less confident about their opinions; this is precisely why we call them non-experts. Conversely, we expect experts to be certain about their opinions, precisely because of their expertise in the field. We find it startling to hear an expert expressing doubt; our violated expectancies increase our interest in the message, and this in turn boosts persuasion (when the message contains strong arguments). So the main takeaway is that lay people should express high certainty and experts should express some doubt. Yet again, here the function of certainty or uncertainty is to create unexpectedness; when people are already motivated to think carefully about the message, additional unexpectedness may have little effect.
- Whitley, Bernard E., Jr. and Martin S. Greenberg , The Role of Eyewitness Confidence in Juror Perceptions of Credibility, Journal of Applied Social Psychology, Vol. 16, 387-409 (1986).
- Sniezek, Janet A. and Lyn M. Van Swol, Trust, Confidence, and Expertise in a Judge-Advisor System, Organizational Behavior and Human Decision Processes, Vol. 84, 288-307 (2001).
- Price, Paul C. and Eric R. Stone, Intuitive Evaluation of Likelihood Judgment Producers: Evidence for a Confidence Heuristic, Journal of Behavioral Decision Making, Vol. 17, 39-57 (2004).
- Elizabeth R. Tenney, Robert J. MacCoun, Barbara A. Spellman, and Reid Hastie, Calibration Trumps Confidence as a Basis for Witness Credibility, Psychological Science Vol. 18, 46-50 (2007)
- Uma R. Karmarkar, Zakary L. Tormala, Believe Me, I Have No Idea What I’m Talking About: The Effects of Source Certainty on Consumer Involvement and Persuasion, Journal of Consumer Research, Vol. 36, 1033-1049 (April 2010)